Extended Defects in GaN: a Theoretical Study
- PDF / 409,268 Bytes
- 7 Pages / 612 x 792 pts (letter) Page_size
- 64 Downloads / 256 Views
J. Elsner, Th. Frauenheim, M. Haugk, R. Gutierrez
Fachbereich Physik, Universitat GH Paderborn, D{33098 Paderborn
R. Jones
Department of Physics, University of Exeter, Exeter, EX4 4QL, UK
M. I. Heggie
CPES, University of Sussex, Falmer, Brighton, BN1 9QJ, UK
Abstract We present density{functional theory studies for a variety of surfaces and extended defects in GaN. According to previous theoretical studies1 f1010g type surfaces are electrically inactive. They play an important role in GaN since similar con gurations occur at open{core screw dislocations and nanopipes as well as at the core of threading edge dislocations. Domain boundaries are found to consist of four{fold coordinated atoms and are also found to be electrically inactive. Thus, except for full{core screw dislocations which possess heavily strained bonds all investigated extended defects do not induce deep states into the band{gap. However, electrically active impurities in particular gallium vacancies and oxygen related defect complexes are found to be trapped at the stress eld of the extended defects.
1. Introduction GaN has recently been the subject of considerable interest due to its optoelectronic properties. In particular the wide band gap (3.4 eV for wurtzite GaN) makes blue light applications feasible. Defect{induced electronic states in the band gap can signi cantly alter the optical performance. This fact becomes extremely important in laser devices, where parasitic components in the emission spectrum are highly undesirable. Moreover, point defects could be trapped in the stress eld of extended defects giving rise to charge accumulated in the vicinity. The resulting electrostatic eld leads to electron scattering which will severely affect the electron mobility (see Look and Sizelove2 for a recent model). Therefore, there is considerable interest in understanding the microstructure of extended defects in GaN and their interaction with point defects. In this paper we present the geometries, energetics and electrical properties of extended defects in GaN using an ab initio local density{functional (LDF) cluster method, AIMPRO, and a self{consistent charge density{functional tight{binding method SCC{DFTB. The latter can be used in large supercells and enables the formation energy of the defects to be found. Details of the methods and their application to GaN and oxygen related defect complexes in GaN have been given previously3{5 and will not be repeated here. 1
Downloaded from https://www.cambridge.org/core. IP address: 5.101.219.98, on 29 Nov 2018 at 22:21:59, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/S1092578300002544
2. Threading Dislocations in GaN A. Threading Screw Dislocations We consider rst a screw dislocation with a full core3. Full core screw dislocations have recently been observed by Xin et al. using the high resolution Z{contrast imaging technique6. The presence of atoms so close to the dislocation axis leads to severely strained bond lengths
Data Loading...
